AHRS

Gimbal lock occurs when pitch reaches 90 degrees (e.g., nose straight up or down); at this singularity, roll and yaw become dependent and one degree of freedom is lost. Avoid by using quaternion representation instead of Euler angles for internal calculations; convert to Euler only for display. Quaternions are singularity-free.

Static initialization (hold still for 1–2 seconds) is simplest. For dynamic initialization, use a longer observation window (5–10 seconds) with a motion model that assumes known maneuvers or low-acceleration. Some systems use GPS velocity to detect motion mode and apply appropriate initialization.

Complementary filter is heuristic and simpler to tune; it high-pass filters gyro rate and low-pass filters accelerometer/compass. Kalman filter is optimal for linear systems and naturally handles different sensor uncertainties. Kalman filter is more robust but computationally heavier. For most applications, complementary filter suffices.

Monitor magnetometer readings for anomalies (magnitude change, deviation from expected field). Compare compass heading with inertial estimate; large disagreement signals disturbance. Mitigation: use a heading estimate from GPS velocity during disturbance, apply soft iron/hard iron calibration, or reduce compass weight in the filter.